Method for ion production

Abstract

A method for producing multiply charged ions is provided. In the method, a laser is used to ablate a sample comprising a matrix and an analyte. The sample is in the liquid form when it is ablated and the ions produced are passed through a heated conduit. The multiply charged ions produced may be used in mass spectrometry to measure the mass of the analyte.

The invention claimed is: 
     
       1. A method for producing multiply charged ions, comprising the steps of;
 i) providing a matrix composition comprising a matrix material and a non-volatile component, 
 ii) providing an analyte, 
 iii) depositing the matrix composition and the analyte on a surface such that they are in intimate contact, 
 iv) ablating the matrix composition and the analyte deposited on the surface with a laser to desorb multiply charged ions of analyte, and 
 v) passing the desorbed multiply charged ions through a heated conduit, 
 
       wherein, in step iv), the matrix composition and analyte are ablated in the liquid phase. 
     
     
       2. The method of  claim 1  wherein the heated conduit is maintained at a temperature of up to 400° C., and is preferably maintained at between 200° C. and 250° C. 
     
     
       3. The method of  claim 1  wherein the heated conduit is a tube. 
     
     
       4. The method of  claim 1  wherein the matrix material of the matrix composition of step i) is either DHB or CHCA or a different cinnamic acid derivative. 
     
     
       5. The method of  claim 1  wherein the matrix composition further comprises a solvent. 
     
     
       6. The method of  claim 5  wherein the solvent comprises a 1:1 mixture of 10-100 mM ammonium phosphate (in water) and methanol. 
     
     
       7. The method of  claim 1  wherein the laser is a pulsed laser and has an energy of less than 10 μJ per pulse. 
     
     
       8. The method of  claim 1  wherein the laser achieves a maximum fluence of less than 2000 J/m 2 . 
     
     
       9. The method of  claim 1  wherein the laser is a pulsed laser, the energy per pulse is about 1-10 μJ and the fluence is between 200-2000 J/m 2 . 
     
     
       10. The method of  claim 1  wherein the analyte is a peptide, protein or other biomolecule or organic compound. 
     
     
       11. The method of  claim 1  wherein the non-volatile component is glycerol, triethylamine or an ionic liquid. 
     
     
       12. The method of  claim 11  wherein the glycerol concentration in the matrix composition is between 15% and 85% by volume. 
     
     
       13. The method of  claim 1  wherein multiply charged ions exiting the heated conduit are passed into a mass analyzer which preferably comprises an ion trap or quadrupole. 
     
     
       14. The method of  claim 13  wherein the analyte concentration in the matrix composition and analyte deposited on the surface is greater than 10 −12  M, the laser is a pulsed laser having a repetition rate of 10 Hz, and data is acquired in the mass analyzer for at least 10 minutes. 
     
     
       15. The method of  claim 13  wherein the analyte amount in the matrix composition and analyte deposited on the surface is greater than 1 attomol, the laser is a pulsed laser having a repetition rate of 10 Hz, and data is acquired in the mass analyzer for at least 10 minutes. 
     
     
       16. A method according to  claim 1  wherein the laser has a UV or IR wavelength.